1. Field of the Invention
The present invention pertains to a device for forming billets made from a flexibly rolled metal band which has at least two different thicknesses and the thickness profile of the billet essentially extends symmetric referred to the central plane of the billet, i.e., the billet contains a thickness transition on both sides, and wherein the thickness transitions are transferred to only one side of the component formed from the billet such that one side of the formed component has a thickness transition and the other side of the formed component is planar. The invention also pertains to a method for forming such billets into such components.
2. Description of Related Art
The billet in question consists of a work piece that is manufactured by flexibly rolling a metal band and subsequently separating the metal band into billets. The flexible rolling method for manufacturing metal bands with band thicknesses that differ over its length in a defined fashion is well known from practical applications and characterized by varying the roll gap in a targeted fashion during the rolling process. In this case, differently long band sections with different band thicknesses are rolled, wherein these band sections may be connected to one another by different inclines such that band thickness transitions are correspondingly produced on both sides. The purpose of the flexible rolling method consists of manufacturing rolled products with cross-sectional shapes that are optimized with respect to the load carrying capacity and the weight. This method is usually realized by rolling the band from coil to coil.
Billets obtained by separating flexibly rolled metal bands consequently have a thickness profile with at least two thicknesses that differ from one another, wherein the regions with different thicknesses are connected to one another by a region that has a predetermined incline, i.e., a band thickness transition. These billets are usually used for manufacturing components with varying wall thicknesses. In this case, the billets typically have a thickness profile that is symmetric referred to the central plane of the billets before they are additionally processed into components with varying wall thicknesses. However, the components to be manufactured from these billets frequently should contain thickness transitions on only one side. For example, when manufacturing a deep-drawn component, only an inner thickness transition or several inner thickness transitions or only an outer thickness transition or several outer thickness transitions should be produced while the respectively other side of the deep-drawn component, i.e., the outer side or the inner side of the deep-drawn component, should be plane. In this case, it is necessary to transfer the thickness transitions that originally existed on both sides to one side of the billet such that one side of the formed billet contains a thickness transition and the other side of the formed billet is plane.
In accordance with the state of the art, the elimination of an undesirable thickness transition or several undesirable thickness transitions is only possible in a separate additional step that either needs to be carried out on the billet that is not yet formed, i.e., before the deep-drawing process, or on the component obtained by means of the deep-drawing process, i.e., after the deep-drawing process. In other words, two steps that differ from one another and need to be carried out successively are required in a device in which the billet is not only subjected to a deep-drawing process, but in which a transfer of the thickness transitions that originally existed on both sides to one side of the billet needs to be realized. This means that the device and the corresponding method are complicated and expensive.
The present invention is based on the objective of providing a method and a device for forming a billet of a flexibly rolled metal band which make(s) it possible to transfer the thickness transitions that originally existed on both sides to one side of the billet in only one step on billets with a thickness profile that essentially extends symmetric with reference to the central plane of the billet, namely such that one side of the formed billet contains a thickness transition and the other side of the formed billet is planar.
The device in accordance with the present invention for forming billets of a flexibly rolled metal band and for attaining the above-mentioned objective essentially is characterized by the fact that the forming surface of the forming device which faces the side of the billet that should contain a thickness transition in the formed state of the billet has a shape that is adapted to the thickness transition to be realized, and by the fact that the forming surface of the forming device which faces the side of the billet that should be plane if the formed state of the billet is plane.
Both sides of the billet manufactured by flexibly rolling a metal band consequently are changed during the forming process in such a way that the thickness transitions which originally existed on both sides are transferred to one side in the same step as the forming process. This means that a thickness transition only exists on one side of the formed work piece, i.e., the formed billet, while the other side is plane. This thickness transition is greater than in the unformed state of the billet, namely twice as large. Although the previous description states that one side of the work piece is plane after the forming process, this does not mean that this side completely lies in one plane. This merely means that no thickness transition exists any longer on this side. For example, if the work piece was, in particular, formed into a deep-drawn component by means of a deep-drawing process, the side of the formed work piece which can also be referred to as the plane side naturally no longer lies completely in one plane, but rather protrudes from the original plane that corresponds to one side of the billet because a deep-drawn component usually consists of a three-dimensional structure. In this respect, the term xe2x80x9cplanexe2x80x9d should be understood as the opposite to the state of one side of the work piece in which this side contains a thickness transition.
The forming device is, in principle, suitable for all known forming methods that serve for forming sheets. Consequently, the invention is also suitable for all conventional types of forming devices. In accordance with one preferred additional development of the invention, it is, however, proposed that the forming devices contain a die and a female mold that cooperate with one another in order to form the work piece. When forming a work piece, the die and the female mold usually cooperate in such a way in that a frame with an opening that is surrounded by the frame is formed by the female mold, wherein the work piece to be formed, i.e., the flexibly rolled billet, lies on the frame such that the region of the billet which lies above the opening of the female mold can be pressed into the opening of the female mold by the die while subjecting the billet to a plastic deformation. Such a combination of a die and a female mold is, for example, used in deep-drawing methods.
Two forming devices, e.g., one die and one female mold, essentially suffice for carrying out the forming method in question. However, one preferred additional development of the invention proposes that the forming devices also contain a holding-down appliance, and that the holding-down appliance has a shape that is adapted to the thickness transition if it is arranged on the side of the work piece which should contain a thickness transition in the formed state, wherein the holding-down appliance is plane if it is arranged on the side of the work piece which should be plane in the formed state of the work piece. Consequently, the holding-down appliance is subject to exactly the same requirements as the other forming devices, e.g., the dye and the female mold, namely that the thickness transitions that originally existed on both sides are transferred to only one side during the forming process due to the shape of the respective component which is either adapted to the thickness transition to be realized or plane.
In one preferred embodiment of the invention in which a die and a female mold are provided as forming devices, the holding-down appliance preferably is arranged on the side of the billet which corresponds to the die such that the holding-down appliance is able to cooperate with the female mold in order to hold down the work piece. This specifically means that the work piece is clamped between the holding-down appliance and the female mold due to the cooperation between the holding-down appliance and the female mold. When processing work pieces with, in particular, a low stiffness, these measures ensure that the work piece cannot completely slide into the opening of the female mold when the die presses the work piece into the opening of the female mold.
In the previous description, it was always stated that the forming device or the forming devices, specifically the corresponding forming surface or the corresponding forming surfaces, which face(es) the side of the work piece that should contain a thickness transition in the formed state of the work piece has/have a shape that is adapted to the thickness transition. A shape of the forming surface of the forming device which is adapted to the thickness transition to be realized is generally utilized if the progression of the forming surface of the forming device exactly corresponds to the obtained progression of the surface of the formed work piece. This means that the surface of the formed work piece is provided with exactly the shape defined by the shape of the forming surface of the forming device. At least slight deviations from this rule are permissible, in particular, in the presence of upsetting effects or hysteresis effects.
With respect to the precise dimensions of the forming surface of a forming device which faces the side of the work piece that should contain a thickness transition in the formed state of the work piece, the general rule applies that, if thickness transitions of a respective thickness d originally existed on both sides of the billet, the forming surface of the forming device needs to contain a thickness transition of essentially the thickness 2d. 
In accordance with the invention, a device of the previously described type is preferably used for a high-pressure sheet forming method, a tension forming method or a tension and compression forming method, in particular, for a deep-drawing method, a stretch-forming method or a pressing method. However, a device in accordance with the invention naturally is also suitable for all other forming methods that operate with two cooperating forming devices.
The method in accordance with the invention for forming billets consisting of a flexibly rolled metal band and for attaining the above-mentioned objective essentially is characterized by the fact that the thickness transitions are transferred to one side of the billet in the step in which the forming of the billet takes place. This is, in particular, possible due to the fact that the transfer of the thickness transition to one side of the billet and the forming of the billet are realized with the same forming devices. Other preferred additional developments of the method in accordance with the invention are realized analogous to the previously described preferred embodiments of the device in accordance with the invention.
There exist various options for designing and additionally developing the device in accordance with the invention and the method in accordance with the invention as will become apparent from the following detailed description of preferred embodiments of the invention in conjunction with the accompanying figures of the drawings.